In mobile communication systems, unicast (point to point (PTP)) transmission is commonly applied to downlink between a user terminal and a base station.
In downlink unicast transmission, the user terminal transmits feedback information related to downlink to the base station. The feedback information is delivery confirmation information (ACK/NACK) indicating whether or not downlink data has been correctly received and channel state information (CSI) indicating a downlink channel state. The base station controls transmission of the downlink data on the basis of the feedback information.
In recent years, multicast/broadcast (point to multipoint (PTM)) transmission has attracted public attention (for example, see Non Patent Literature 1).
In downlink multicast/broadcast transmission, the base station transmits the same downlink data (hereinafter referred to appropriately as “multicast/broadcast data”) to a plurality of user terminals using the same downlink radio resources. The multicast/broadcast transmission can improve use efficiency of the downlink radio resources, compared with the unicast transmission.